A floorboard fitted with a projecting metal strip formed with a locking element for mechanical joining is described in WO 94/26999, which document is herewith incorporated by reference and to which reference is made for a more detailed description of how such building boards can be designed and joined together. The background, features and advantages of the invention will be described for this known type of floorboard, but it should be emphasised that the invention is useful for making building board types other than floorboards, such as wall panels and roof slabs.
WO 94/26999 describes a system for mechanical joining of floorboards. A first mechanical connection provides mutual vertical locking of the joint edges and may be in the form of a tongue-and-groove joint along the joint. A second mechanical connection provides mutual horizontal locking of the boards in a direction at right angles to the joint edges of the boards.
In order to illustrate the problems which form the basis of the present invention, reference is now made to FIG. 1, which shows in section a joint between two identical, mechanically joined floorboards 2. The design and function of the floorboards 2 substantially correspond to what is known from WO 94/26999. However, there are certain differences compared to the prior art with respect to the geometrical shapes of a gripping stud and a locking element. However, these differences are not primarily relevant to this description.
Each board 2 has a top side 4 and an underside 6 and, for illustration purposes, can be assumed to be made of a body S of e.g. laminated fibreboard, plastic composite, wood or the like. The thickness of the body S can, for example, be 7 mm. To enable a mechanical connection, opposite joint edges 8 of the boards 2 are formed with an integrated metal strip 10 mounted at the factory, as well as a locking groove 16. The strip 10 is preferably made of sheet aluminium and extends horizontally from the underside 6 of the board 2 in the direction of the second floorboard and runs continuously throughout the entire length of the joint. However, the strip 10 can be divided into smaller parts, which cover the main portion of the length of the joint.
In the embodiment shown by way of illustration in FIG. 1, the strip 10 is mechanically fastened to the body S in the manner described in more detail below. Mechanical fastening is preferred, but not absolutely necessary for the implementation of the present invention. As an alternative, the strip 10 can be glued or be attached to the body in some other way. However, mechanical fastening is preferred for tolerance reasons. Other sheet metal materials can be used besides sheet aluminium. In order to achieve the required joint tolerances as well as simple laying, the strip 10 is integrally formed with the board, i.e. it is mounted at the factory and should specifically not be mounted in connection with laying. As a non-restrictive example, the strip 10 may have a width of about 30 mm and a thickness of about 0.6 mm.
The strip 10 is formed with a locking element 12, bent from the sheet material, which exhibits an active locking surface 14 having a height of e.g. 1 mm. In the joined state, the locking element 12 is received in a locking groove 16, formed in the underside 6 of the second board and extending parallel to and spaced from the joint edge 8. The locking element 12 and the locking groove 16 together form the above-mentioned second mechanical connection, locking the boards 2 to each other in the direction designated D2. More specifically, the locking surface 14 of the locking element 12 serves as a stop with respect to the surface 18 of the locking groove 16 closest to the joint edges 8.
When the boards 2 are joined together according to FIG. 1, they can occupy a relative position in the direction D2 where a small play .DELTA., as small as 0.01 mm, exists between the locking surface 14 and the locking groove 16. This play .DELTA. makes it possible to displace the boards 2 in the direction of the joint without the use of tools. This displaceability facilitates the laying and enables joining together the short sides by snap action. Reference is made to WO 94/26999 for a more detailed description of the function and advantages of this construction.
The strip 10 is mounted in a tolerance-equalising groove in the underside 6 of the board 2. In this embodiment, the width of the equalising groove is approximately equal to half the width of the strip 10, i.e. about 15 mm. The functioning of and different ways of forming the equalising groove are described in detail in WO 94/26999 and, consequently, need not be repeated here.
For the mechanical fastening of the strip 10 to the board S, a groove 20 is provided in the underside 6 of the board 2 spaced from a recess 22 adjacent to the joint edge B. The groove 20 may be formed either as a continuous groove extending throughout the entire length of the board 2, or as a number of separate grooves. Together with the recess 22, this groove 20 defines a dove-tail gripping stud 24. In its fastened state in FIG. 1, the strip 10 exhibits a number of punched and bent tongues 26 as well as one or more lips 28, which are bent round opposite sides of the gripping stud 24.
The present invention is based on (i) the fact known per se that a good joint of the type described above requires the locking surface 14 to have an exact, predetermined distance from the upper joint edge 8 of the floorboard 2, and (ii) an insight that there are tolerance problems (compound tolerances) which are difficult to overcome in manufacturing the board 2 and the strip 10 as well as in attaching these two components to each other.
The problem behind the invention will now he described in more detail with reference to FIG. 2 in the appended drawings, where the following positions P1-P3, distances S1-S3, and tolerances t1 and t2 are indicated on a finished floorboard 2 according to FIG. 1:
P1-P3 refer to relative positions horizontally.
P1: The upper joint edge 8 of the floorboard PA1 P2: Reference point on the gripping stud 24 PA1 P3: Locking surface 14 of the strip 10 PA1 S1* Desired distance between P1 and P2 PA1 S1 Actual distance between P1 and P2 due to t1 PA1 .+-.t1 Range of tolerance for S1 when milling the gripping stud 24 PA1 S2* Desired distance between P2 and P3 PA1 S2 Actual distance between P2 and P3 due to t2 PA1 .+-.t2 Range of tolerance with respect to P2's position in relation to P3 due to inexact positioning when attaching and manufacturing a preformed strip. PA1 S3* Desired distance between P1 and P3 PA1 S3 Actual distance between P1 and P3 PA1 A. forming the locking surface against a forming surface and then keeping the locking surface thus formed fixed relative to the forming surface until the two steps A and B have been carried out, PA1 B. attaching the strip to the body,
With the above designations, the following applies: EQU S1=S1*.+-.t1 (1) EQU S2=S2*.+-.t2 (2) EQU S3=(S2*.+-.t2)-(S1*.+-.t1)=(S2*-S1*).+-.t1.+-.t2=S3*.+-.t1.+-.t2(3)
Two extreme cases 1 and 2 are found on the basis of these designations:
Extreme Case No. 1: S1 max & S2 min
In a first extreme case, because of inexact milling and/or wear of the milling tool, the gripping stud 24 is maximally displaced (+t1) from its nominal position in the direction away from the joint edge 8. In this case, the distance S1 assumes its maximum value S1*+t1 (P2 far from P1). The strip 10 with preformed locking element 12 is made in such a way and mounted in such a way that the locking surface 14 assumes a position P3 maximally displaced (+t2) towards the gripping stud 24. The distance S2, then assumes its minimum value S2*-t2 (P3 close to P2). In this extreme case, the two tolerances t1 and t2 contribute to the displacement of the locking surface 14 (P3) in the direction towards the upper joint edge 8 (P1). As a result, the locking surface 14 may end up being so close to the upper joint edge 8 that two boards cannot be joined together correctly, or they can become so biased that they cannot be displaced in relation to each other without the use of tools.
Extreme Case No. 2. S1 min and S2 max
In a second extreme case, because of inexact milling and/or wear of the milling tool, the gripping stud 24 is instead maximally displaced (-t1) from its nominal position in the direction towards the joint edge 8. In this case, the distance S1 assumes its minimum value S1*-t1 (P2 close to P1). The strip 10 with preformed locking element 12 is made in such a way and mounted in such a way that the locking surface 14 assumes a position P3 maximally displaced (+t2) from the gripping stud 24. The distance S2 then assumes its maximum value S2*+t2 (P3 far from P2). In this second extreme case, the two tolerances t1 and t2 instead contribute to the displacement of the locking surface 14 (P3) in the direction away from the upper joint edge 8 (P1). As a result, the locking surface 14 may end up too far away form the upper joint edge 8, so that a play exists between two joined boards.
The problem which the present invention aims primarily to solve is the above-illustrated problem of compound tolerances (t1+t2). When the tolerances of the gripping stud 24 are added to the manufacturing tolerances of the strip 10 and the strip/board positioning tolerances, the total tolerance becomes too high and the quality of the system is reduced. If the distance between the upper joint edge 8 and the locking surface 14 is too great, the finished joint will have a gap that is too large. If the same distance is too small, the boards cannot be joined together.
As will be seen from the description below, other advantages in terms of production, in addition to the elimination of the above-mentioned problem of compound tolerances, are achieved by the present invention.
In order to solve the aforementioned problems, the invention provides a method according to claim 1 as well as equipment according to claim 15, preferred embodiments being stated in the dependent claims.
Thus, the invention provides a method and equipment for making building boards of the type comprising a body fitted with a locking device in the form of a strip extended from the body with a formed locking surface for mechanical joining of the boards, the strip and the locking surface being formed in one piece from a blank. The invention is characterised by carrying out the following steps A and B in optional order:
and by, during the implementation of the latter of the steps A and B, keeping the body fixed against a reference surface, whose position relative to the forming surface corresponds to a desired position of the locking surface relative to the body.
Within the scope of the above definition of the invention, there are a number of embodiments, which all achieve the desired accuracy of the distance between the locking surface and the body. In every case, the invention is characterised in that the strip never is both formed with its locking surface and attached to the body prior to positioning the locking surface and the body correctly in relation to each other with the aid of the forming surface and the reference surface. Regardless of the order in which the steps A and B are carried out, the aforementioned problem of compound tolerances is eliminated.
According to the definition of the invention, when the locking surface has been formed, the strip is never handled as a completely separate unit during the manufacturing process and, preferably, nor is the strip handled as a separate unit before the locking surface is formed.
Using a store of separate, preformed and/or unformed strips entails undesired handling and positioning problems. The strip, with or without a formed locking surface, should always be fixed in relation to at least one of the forming surface, the body, and the blank.
In order to implement the invention, the strip is preferably mechanically attached to the body, but gluing is also possible. Preferably, the strip is mechanically attached by bending certain parts of the strip round a gripping stud formed in the body, for example as disclosed in WO 94/26999.
According to a preferred embodiment of the invention, the blank is gradually fed forward and is subsequently divided for separating the strip from a subsequent part of the blank, which is gradually fed forward during a subsequent cycle. Preferably, the blank is not divided until the strip has been fixed in relation to the forming surface and/or has been attached to the body.
The forming surface and the reference surface preferably constitute two surfaces in one and the same pressing or punching tool.
According to a first alternative, the strip is attached to the body before the locking surface is formed against the forming surface. In this case, it is possible to attach the strip at a different location and subsequently arrange the body with the attached strip in a forming tool for forming the locking surface, while holding the body fixed against said reference surface. However, it is preferred to carry out the attaching and forming in one and the same tool without intermediate handling of the strip and the body.
According to another alternative, the locking surface is formed against the forming surface before the strip is attached to the body, the formed locking surface being held fixed relative to the forming surface until the attachment step has been carried out.
According to a particularly preferred embodiment, the locking surface is formed against the forming surface and the strip is attached to the body in one single reciprocating punching operation of a punching tool common to these two steps. In this case, no handling of the strip and the body is required between the steps A and B. The forming and the attaching can be effected essentially simultaneously, but, preferably, the strip is attached to the body somewhat prior to the forming of the locking surface.
The body exhibits an edge portion which, in the case of mechanical joining of the board to a second board, lies in the immediate vicinity of the second board. The step of fixing the body against the reference surface preferably comprises positioning and fixing this edge portion against said reference surface, whose position in relation to the forming surface corresponds to a desired position of the locking surface in relation to said edge portion. Other portions of the body are also possible, but might provide an inferior final result because of tolerance problems.
To sum up, the inventions affords, inter alia, the following advantages: A building board of the type in question, for example in the form of a floorboard, of e.g. 1200*200 mm, can, on one long side as well as on one short side, be provided with a formed and attached strip a) in one single manufacturing operation, b) in a continuous process, c) with a very short cycle time of about 2 s, and d) within tolerances of .+-.0.01 mm between the locking surface and the joint edge despite the fact that, in practice, the manufacturing tolerances are considerably larger. In general, in manufacturing, it is desirable to be able to work with the largest possible tolerances, since this reduces set-up and take-down times, checks, and tool grinding.
The aforementioned as well as other embodiments and advantages can be seen from the claims and the description hereinbelow of a preferred embodiment of the invention.